1. Field of the Invention
With reference to the classification of art as established in the United States Patent and Trademark Office the present invention is believed to be found in the general Class entitled, "Package Making" (Class 53) and in the subclasses thereunder entitled, "methods-with contents treating-vacuum or gas receptacle forming" (subclass 22A) and "with contents material treating-vacuum or inert atmosphere -- includes container forming" (subclass 112A).
2. Description of the Prior Art
The apparatus, the method of vacuum forming and packages formed while in a vacuum chamber are all well known. Film packaging of food products is particularly a well known and crowded art since todays fresh meat, produce and many frozen products are delivered to the stores in an already film packaged state. Toward that end and to the extent applicable to this type of package, reference is made to U.S. Pat. No. 3,491,504 as issued to W. E. YOUNG, etal. on Jan. 27, 1970 and to U.S. Pat. No. 3,686,822 as issued to WOLFELSPERGER on Aug. 29, 1972. In these and many other patents warmed film is drawn to and around the product by the influence of atmosphere as and after the package and contents have been brought to a condition of reduced pressure while in a vacuum chamber. In these patents and in other apparatus the sealing occurs within the chamber. In many skin packages the film material is stretched to the point where it loses its barrier properties which protect the product from moisture losses and from oxygen. Automatic skin packaging of many products, therefore, is often less than satisfactory in producing sound packages.
In the present invention the problem or excess film, that is film which is not utilized in encasing the product, is solved by providing a double ended bag. After the product is positioned in the tubular film member, a pair of spreader probes is moved by pneumatic means away from each other to cause a narrow elongated opening to be formed at and in each end of the tubular film. These probes enter both ends of the tubular film. The spreader probes, as they move apart, lightly stretch each end opening and more-or-less center the openings with the center line of the tubular film. The film is heated while the product encased in the tubular film is transported to a vacuum chamber and the apart spreader probes are maintained in the tubular film. Prior to closing and evacuating the vacuum chamber, the pair of spreader probes are withdrawn directly outward in order to maintain the elongated opening at each end of the film. This stretch maintains the opening while the chamber is closed and brought to a condition of reduced pressure. After the desired amount of reduced pressure is achieved, the elongated end portions of the film are sealed by sealing bar means. The ends of the film are heated by local heaters within the chamber and these ends may or may not remain clamped during venting of the chamber. The chamber is then opened to atmospheric pressure and the vacuum packaged and sealed product is removed from the vacuum chamber. A pressure differential across the packaging film causes the heated film to be stretched and formed about the end of the product.